Ceramics are inorganic solids which are characterized by hardness, brittleness (non-ductility), and heat resistance (refractoriness). Ceramic objects are manufactured by subjecting powdered starting materials to a high temperature and pressure processing stage. Ceramics can operate at temperatures above those at which metals lose significant residual strength, while retaining useful attributes including resistance to abrasive wear and to many chemical environments. However, ceramics do not exhibit strength under tension and often act in a brittle or non-ductile manner. The brittleness is usually caused by crevices and faults on the surface or within the material, from which the fracture process commences on applying a stress. Therefore, it is desirable to join or bond a ceramic component functioning at high temperature to structures or moving parts which must withstand stresses too great for ceramics and must consequently be metals.
A ceramic-metal bond can be achieved through mechanical joining, such as with metal hooks or dog bones, or through press and shrink fitting. Alternatively, a metal coating can be placed on the ceramic part through plasma spraying. However, there is a limit to the thickness of the material that can be applied in this manner. Another technique which has been used to bond a metal and a ceramic is brazing. This technique can be more expensive as it requires a brazing metallization layer such as molybdenum or molybdenum-manganese. Additionally, the strength of the bond cannot easily be varied or controlled, and the bonding process is an additional step in the fabrication of the bonded component.
Accordingly, prior to the development of the present invention, there has been no method of bonding a ceramic part to a metal part so that the bond strength can be controlled, and so that the metal part and the bond can be formed concurrently. Therefore, it is an object of the present invention to provide a method of bonding a ceramic part and a metal part so that the bond strength can be controlled. It is a further object of the present invention to provide a method of bonding a ceramic part and a metal part so that the fabrication of the metal part and of the bond can be done concurrently. It is a feature of the method of the present invention that the bond strength can be controlled through choice of the material for the metal part, and by varying the effective surface area of the bond interface region.